Great Tits have increased steadily since the 1960s,
with the exception of two brief periods of stability or shallow
decline during the mid 1970s and late 1980s. Recent CBC/BBS
and BBS results suggest that this increase is continuing, in
all UK countries. More widespread food provision in gardens
during winter is one possible explanation for the increase.
Alongside population increase there has been a long-term decline
in productivity, as measured by CES. A small but significant
fall in the number of fledglings per breeding attempt suggests
that the reduced numbers of juveniles result from lower productivity
of individual attempts rather than from changes in the number
of breeding attempts or in post-fledging survival rates. Laying
date has advanced by about a week in the UK, in line with climatic
change. In a Dutch study population, however, the breeding period
did not advance during 1973–95 and became increasingly
mistimed with respect to the peak of insect abundance (Visser
et al. 1998).